1. Field of the Invention
The present invention relates to a hydraulic turning joint, and more particularly, to a hydraulic turning joint used for jointing upper and lower frames of equipment such as excavators, cranes, etc., wherein the upper frame is swingably jointed to the lower frame.
2. Description of the Prior Art
In construction equipment such as excavators or cranes, an upper frame is swingably jointed to a lower frame and for this jointing, a hydraulic turning joint is used as a jointing means.
More particularly, the hydraulic turning joint should joint the upper frame and lower frame of equipment such that not only the upper frame can be rotated smoothly relative to the lower frame, but also oil can flow between the upper and bottom frames through the hydraulic turning joint. That is, the hydraulic turning joint should provide an oil passage for the supply of a pressurized oil discharge from a hydraulic pump installed on the lower frame, to an actuator of each working member (in case of the excavator, a boom, an arm, a bucket, etc.) installed on the upper frame.
In a conventional hydraulic turning joint, as shown in FIG. 1, a shaft 102 coupled to a lower frame is rotatably and closely accommodated within a housing 101 coupled to an upper frame. The inside of the shaft 102 is formed with a plurality of oil supply passages 103a.about.103e, and the housing 101 is formed with a plurality of oil discharge passages 104a.about.104e, each of which is in communication with each of the above mentioned oil supply passages 103a.about.103e. Furthermore, sealing slots 105a.about.105c are formed at various places (between the oil passages) of the inner circumferential surface of the housing 101 to provide a seal, and since the sealing members 106a.about.106c are mounted in the sealing slots 105a.about.105c, the sealing action can be performed between each of the adjacent oil passages 104a.about.104e. By means of the hydraulic turning joint constructed as mentioned above, not only the upper frame can be swingably jointed to the lower frame, but also the oil can flow between the lower frame and the upper frame.
However, conventional hydraulic turning joints as mentioned above have the disadvantages that, as the number of the oil passages in creases, the longitudinal length of the hydraulic turning joint becomes longer than its transverse length. As a result, it is difficult to have enough space for mounting the above mentioned hydraulic turning joint in the equipment.
Further, conventional hydraulic turning joints have another disadvantage that, since the length of the housing is relatively longer than the diameter of the housing 101, the inner circumferential surface of the housing 101 has to be machined from both ends to the central section of the housing 101, rather than be machined at a time through either the top end or the bottom end. This creates a degraded roughnecks on the inner circumferential surface, resulting in increased work time to finish the surface, a reduction in work efficiency and a possible lowering in the reliability of the entire product.